On Sun, 11 Nov 2007 17:14:45 +0000 (UTC), danny burstein wrote:


You might have heard the screams about five years
ago when Sony's camcorders, when in "nightshot"
mode, could "see through clothing". THe reality
is that the sensors could pck up "near infra-red".

Many materials that look "black" are really very, very,
dark red - letting a teensy bit of visible red
through (so small it looks blackish) but a modest
amount of near infra-red. So these cameras could
kind of, in some instances, maybe... look "through"
those fabrics - if they were thin enough.

That camera and any other with the IR cut filter removed and a low pass optical
filter installed work (quite well, actually) to image through clothes for the simple
reason that many fabrics are transparent to shortwave IR. The camera doesn't image
body heat. It images reflected IR that passes through the cloth. Cotton and wool
are essentially opaque. Light synthetics like rayon are transparent.

John
--
John De Armond
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http://www.neon-john.com
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Tellico Plains, Occupied TN
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